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When you think of Concord, MA, you’re more likely to visualize Revolutionary War skirmishes or Thoreau’s cabin on Walden Pond than factories full of complex machinery. But in fact, Concord was once a major hub of the clockmaking industry—in 1800 there were at least seven well-known clockmakers in the city, along with a network of suppliers including brass foundries, iron forges, wire mills, and cabinet builders. And as I learned during a recent visit to display maker Prysm, whose facility sits just across an abandoned railroad right-of-way from the Massachusetts Correctional Institute, the manufacturing spirit is alive and well in Concord.

At the core of Prysm’s plant—in a clean room that I was only allowed to visit after putting on a gown, shoe covers, and a hairnet—are four large screenprinting machines that are in nearly continuous operation, churning out the rubbery layers of phosphor material that make up the heart of Prysm’s displays. The way the company’s engineers explain it, the machines work just like those used to print designs on T-shirts—except that the phosphor stripes on Prysm’s screens are just millimeters wide, are made of exotic chemicals that glow red, green, or blue when exposed to laser light, and must be positioned with absolute precision. Which is not too different from clockmaking, when you think about it.

“Our first printing machine wasn’t even in a clean room,” says my host, Patrick Tan, Prysm’s vice president of panel development and manufacturing. “It was in the old Clock Tower Place mill building in Maynard, directly below the offices of Monster.com. Any time they had a party, it would rain wood fibers. We lived with that for as long as we could, but eventually we had to move—and that’s why we’re here in Concord.”

The startup finished that move last August, back when it was still known by its stealth name, Spudnik. It wasn’t until this January—almost five years after its founding by Boston University alums Roger Hajjar and Amit Jain—that the company finally lifted the veil on its technology, which it calls the laser phosphor display, or LPD. As I wrote in one of the first published profiles of the company, Prysm has big plans to use this old-meets-new technology to disrupt the market for large-format displays—that is, the wall-sized displays used for trade shows, stage productions, train station departure-time screens, and Times Square billboards.

Prysm’s current product isn’t huge by the standards of today’s flat-panel displays—it’s a 25-inch-diagonal screen, code-named Maui. But the screen on the Maui has no bezel, which means the units can be lined up edge-to-edge and stacked vertically to form a single, nearly seamless display of any required size. And perhaps the biggest selling point for the new display is that it’s driven by highly efficient lasers—the same commodity blue-violet lasers, in fact, that are found inside Blu-ray players. LPDs therefore use far less electricity than today’s dominant technology for large-format displays, arrays of light-emitting diodes (LEDs).

“Our first targeted application is for large indoor venues like airports, train stations, shopping malls, and convention centers, where LED displays are fairly entrenched today,” says Tan, a veteran of Digital Equipment Corporation (DEC). “One of the big problems with LED installations is that the first order of business is to get Tony the electrician to install power, they’re such big power consumers. For us, we should be able to run off of wall sockets.” A 142-inch screen that Prysm demonstrated recently in Amsterdam (shown in the picture here) used no more power than a microwave oven, Tan says.

The part of the Maui unit that’s being manufactured in Concord, inside a 32,000-square-foot building that formerly housed a maker of components for electron microscopes, is the business end—namely, the phosphor-covered layer of glass where the picture shows up. Other parts of Prysm’s devices are made in Bangalore, India, and the finished displays are assembled at the startup’s headquarters in San Jose, CA.

Tan and his colleagues gave me a comprehensive tour of the lab spaces where Prysm’s 35 Concord-based employees are building and testing the screens. So comprehensive, in fact, that it included many of the “secret sauce” particulars that tech companies are usually loath to reveal to anyone, let alone journalists. In exchange for this rare glimpse behind the scenes, I agreed to gloss over some of the key details in this writeup.

John Ritter, senior director of process development at the Concord plant, spends a lot of his time in the clean room. He explained to me that the job of the screenprinting devices—by far the most expensive machines in the building—is to deposit thin stripes of material on the ribbed polymer mats at the heart of the Prysm screens. There are four machines: one for the red phosphor stripes, one for blue, one for green, and one for the glue used to bond each mat to a base layer of glass.

If you look closely at a finished Prysm screen, you can make out the individual red, green, and blue stripes, which are reminiscent of the phosphors on the inside surfaces of the cathode ray tubes in old-fashioned televisions. This is part of what I mean when I call Prysm’s technology “old meets new.” The beauty of Prysm’s laser phosphor technology is that the screens have no fixed pixels. Rather, a tiny dot of color shows up whenever a laser beam strikes one of the phosphor stripes, in much the same way that the phosphor dots in a CRT light up when struck by an electron beam. This way, there’s no need for the complicated, expensive, finicky array of switches and transistors that drives the individual pixels in a flat-panel LCD or LED display (the so-called “backplane”).

Of course, if you want to draw a high-definition video image on an LPD screen at 30 frames per second, some fancy engineering is required to direct the laser beams to the right spots. That’s the job of the so-called “light engine” portion of the Maui units. The light engines aren’t manufactured in Concord, but Tan showed me around a testing lab where several of these engines were in various states of dishabille. They resemble compact versions of the tabletop optics experiments your high-school physics teacher probably showed you, with lots of lasers, lenses, and mirrors.

The core of the light engine is an array of indium-gallium-nitride laser diodes, which emit coherent beams of light at the same 405-nanometer wavelength used in Blu-ray players. There have been many previous attempts to build laser-driven displays, but the real “aha” moment that gave Prysm’s founders hope for their own technology, senior director of systems and test engineering Dave Kent told me, was the realization about five years ago that the laser diodes then being developed for optoelectronic storage devices like Blu-ray players would be perfect for display applications. Not only would these lasers be relatively cheap, since there were already plans to mass-produce them for Blu-ray players, but they are “modulatable,” meaning their power levels can quickly be turned up, down, or off, which is obviously important for projecting a moving image on a screen.

The next key component of the Prysm light engine is a spinning, multifaceted mirror. (To learn just how many facets the mirror has, or how many lasers are in the Prysm array, you’ll just have to buy a Maui unit and tear it down. Those are the sorts of details I agreed not to specify.) The function of the spinning mirror is to direct a bundle of laser beams to a specific group of targets on the phosphor stripes, then quickly redirect the beams to the adjacent set of targets, and so forth, many, many times each second.

Of course, there’s a whole obstacle course of other mirrors and lenses in between the spinning mirror and the phosphor panel—including a Fresnel lens bonded to the panel itself that intercepts the laser beams and straightens them out so that they hit the phosphor stripes at right angles. There’s also a control layer bonded to the panel, etched with lines that resemble a bar code; the system uses the reflections from this so-called “servo layer” as a form of feedback, constantly adjusting the aim and timing of the laser beams to stabilize the picture and make sure that the laser beams are hitting the correct phosphor stripes.

Remarkably, Prysm’s engineers have figured out how to squeeze the entire optical mechanism into a box only about 18 inches deep. One trick for providing the laser beams with all the focal length they need was to use a periscope-like set of mirrors to add height to the units rather than depth; these give the Maui a zig-zag shape that make the units not only shallower but more stackable.

As innovative as its overall concept may be, however, Tan says Prysm uses as much off-the-shelf technology as it can, starting with the laser diodes. “As you dream of how to design something, you’ve got to be sure you can make it,” he says. “We try to avoid the NIH [Not Invented Here] syndrome—if it’s already been solved elsewhere, we use it.”

Tan is also proud of Prysm’s green credentials. In fact, the company has coined a word, “ecovative,” to underscore its commitment to building devices that don’t use much energy compared to traditional displays, and that don’t contain any heavy metals or toxic gases. “We’re trying to come up with something that addresses the limitations [of traditional large-format displays] but at the same time make it as eco-friendly as possible,” Tan says.

Under the Spudnik name, Prysm raised an unspecified amount of Series A venture funding in late 2005, and then a larger Series B round in the spring of 2007, according to Tan. Its investors have included Partech International, Artiman Ventures, CSK Group, and the now-defunct Galleon Group.

The next big milestone for the startup, before it can win some big commercial installation projects, will be showing that the 25-inch Maui screens can be stacked and tiled up to any required size. The biggest display the startup has attempted to assemble to date is a 12-by-12 array of Maui screens with a total diagonal measurement of 300 inches, or 25 feet. The challenge of going bigger isn’t really a mechanical one right now, Tan says—it’s more a matter of improving the tiling software that takes a single video signal and spreads it across the 12-by-12 array’s 144 separate screens.

“You have to prove mechanically that the screens can go together, and electrically that you can take a signal, split it up, recombine, and have it look good,” says Tan. “If we put some effort into it, we can make something much bigger. We’d just have to scale the tiling engine and work on the packaging a bit, but basically it’s like stacking Lego blocks.”

With plenty of expertise on hand—including seven staffers with PhDs in chemistry, physics, and optics, along with others who have spent time at legendary New England technology organizations like DEC, Polaroid, and MIT’s Lincoln Laboratory—Tan seems confident that the startup can figure out how to put all the pieces together.

“Having the capability and knowledge is one thing, but you’ve also got to deliver, and many of us have worked in companies that have delivered product to the marketplace,” Tan says. “We’re all good problem solvers. If you ask why Japan Inc. didn’t come up with [the laser phosphor display], I think it’s because you can get optimized around a space and forget to take a step back. I think this is where the U.S. is terrific. You have smart, playful engineers who say, ‘Why not?'”